Using microiontophoretic and single-cell recording techniques, the effect of chronic lithium (Li) treatment on the development of supersensitivity to dopamine (DA) was investigated on DA-containing cells in the zona compacta region of the substantia nigra in the intact rat. Supersensitivity, as measured by increased sensitivity to iontophoretically applied DA and to the i.v. administration of graded doses of the DA agonist apomorphine, was observed in presynaptic (DA-containing) cells following chronic haloperidol (HAL) administration. Animals treated chronically with both Li an HAL failed to show any increase in sensitivity to either iontophoretically applied DA or to i.v. apomorphine.